The present invention concerns bipolar electrodes for electrolysis cells of the filter-press type, in which the cathode and/or anode frames have been incorporated.
Bipolar electrodes are known to have the advantage of permitting compact construction in electrolysis cells and an ease of feeding of electricity due to the electrical connection in series of the unit cells formed by the succession of electrodes. These electrodes are characterized by the fact that their two active portions are separated in space, and by a careful assembling of these two portions which permits the passage of electricity of high density with very low ohmic or resistance losses.
While the general characteristics of cells of the filter-press type have been known for a long time, the materials used heretofore for the construction of the electrodes, joints, frames or diaphragms did not make it possible to obtain reliable operation of such cells.
In recent years, the reliability of these complex assemblies and the electrical charge per unit of surface of electrode have been improved by the use as electrodes of metal structures the construction of which include titanium and homologous metals, such as the film-forming metals, the anode portions of these structures being covered with conductive active layers having a base of noble metals or oxides of said metals, which are not attacked by the electrolyte.
Such bipolar electrodes have been described in particular in Copending Buoy et al. U.S. patent application, entitled "Bipolar Electrodes," filed on Dec. 13, 1972, under Ser. No. 314,728, now U.S. Pat. No. 3,859,197. The anode portion consists of titanium covered with a conductive active layer and the cathode portion is of mild steel. These electrodes are characterized by the fact that these two portions are separated in space, at least one of them being perforated, and by the fact that the electrical connection between these two portions is effected via the contact formed by the cladding of the titanium on the mild steel. The mechanical connection between these two active portions and the mixed parts thus formed by cladding is obtained by plates or shaped parts of titanium and of plates of mild steel.
However, the construction of filter-press cells of high productivity employing these electrodes raises difficult problems of gas-liquid separation and of flow of the electrolyte. In order to avoid the possible disadvantages, copending Buoy et al. U.S. patent application, entitled "Frames for Electrolytic Cells of the Filter-Press Type," filed on Dec. 13, 1972, under Ser. No. 314,817, now U.S. Pat. No. 3,836,448 discloses frames consisting of two distinct zones, a low zone contemplated to receive an anode or a cathode and a high zone in the form of a closed box contemplated to assure the separation of the electrolyte and the gases produced during the electrolysis.
The use of electrolytically active portions, at least one of which is provided with holes or perforations, requires the presence of a partition between these two portions in order to avoid attack of the electrolytically active portions or avoid the mixing of the anolyte with the catholyte. Such a partition can be formed of a metal wall which may have two faces of different materials which, however, are not attacked by the electrolyte with which each of them is in contact.
The two portions being separated in space, it is necessary to assure good rigidity and good planarity of the assembly, in particular as the interpolar distance between successive electrodes must be constant and reduce to the minimum, so as to make possible the use of a prefabricated diaphragm.